O2 sensor values on CCR dives

[Jef Driesen]

On 2017-12-02 22:39, Anton Lundin wrote:
> On 02 December, 2017 - Anton Lundin wrote:
>> I saw something odd looking at that data. There's another calibration
>> value in the data, which we never figured out the meaning of.
>> 
>> In all other sample data its bin zero or low values like 2. In your 
>> data
>> its 255.

I assume you are talking about the ADC offset field?

>> The thing is also that if i "correct" your mV values by about -8, the
>> data lines up pretty nicely, so there's some correcting needing to be
>> done.
>> 
>> Can you save the same dive from Shearwater Desktop so I can take a 
>> look
>> at the mV values they report there, so see of they are out by about -8
>> or so?

The sensor millivolt values in the xml export and the raw data seems to 
be identical. At least for the few I checked. So I don't think we have 
to look there.

> What I've guest previously, is that the unknown parameter there is
> related to O2 Offsets.
> 
> Some related material on the subject is from when a production mis
> caused them to be left as zero:
> https://www.shearwater.com/wp-content/uploads/2016/07/O2-Offsets-Public-Notice-RevA.pdf
> 
> Why your's are max value 255 (signed -127), I don't know but they might
> be just that.
> 
> What we never knew earlier was the unit of the offset value, or if it
> was already applied to the value stored in the log.

Just a minor correction: When interpreted as a signed 8 bit number, the 
value 255 is -1, not -127.


Anyway, I analyzed all the data I have available and listed the 
calibration values stored in the dive header. The results are shown 
below.

The numbers are respectively:
  * sensor voting status bit (at offset 16)
  * calibration status bit (at offset 86)
  * calibration value (at offset 87-92)
  * adc offset (at offset 93-95)

perdixai.jongross
Sensor 0: 0 0 2100 -1
Sensor 1: 0 0 2100 -1
Sensor 2: 0 0 2100 -1

perdixai.linustorvalds
Sensor 0: 0 0 2100 -1
Sensor 1: 0 0 2100 -1
Sensor 2: 0 0 2100 -1

perdix.alvaroaguilera
Sensor 0: 0 0 2100 -1
Sensor 1: 0 0 2100 -1
Sensor 2: 0 0 2100 -1

perdix.timmassey
Sensor 0: 0 0 2100 -1
Sensor 1: 0 0 2100 -1
Sensor 2: 0 0 2100 -1

petrel.davidedb.310d20b4 (CCR, extppo2)
Sensor 0: 1 1 2100 -1
Sensor 1: 1 1 2100 -1
Sensor 2: 1 1 2100 -1

petrel.davidedb.39117da9 (CCR, extppo2)
Sensor 0: 0 1 2100 -1
Sensor 0: 1 1 2100 -1
Sensor 1: 0 1 2100 -1
Sensor 1: 1 1 2100 -1
Sensor 2: 0 1 2100 -1
Sensor 2: 1 1 2100 -1

petrel.henrikaronsen
Sensor 0: 0 0 0 -5
Sensor 0: 0 0 2100 -5
Sensor 1: 0 0 2100 -27
Sensor 1: 0 0 2148 -27
Sensor 2: 0 0 0 -9
Sensor 2: 0 0 2100 -9

petrel.jimpiavis
Sensor 0: 0 0 2100 -1
Sensor 1: 0 0 2100 -1
Sensor 2: 0 0 2100 -1

petrel.nickshore
Sensor 0: 0 0 2100 13
Sensor 1: 0 0 2100 11
Sensor 2: 0 0 2100 -23

petrel.stevewilliams (CCR, extppo2)
Sensor 0: 0 0 2100 2
Sensor 0: 0 1 1986 2
Sensor 0: 1 1 1769 2
Sensor 0: 1 1 1793 2
Sensor 0: 1 1 1826 2
Sensor 0: 1 1 1879 2
Sensor 0: 1 1 1935 2
Sensor 1: 0 0 2100 16
Sensor 1: 0 1 1970 16
Sensor 1: 0 1 2229 16
Sensor 1: 1 1 2227 16
Sensor 1: 1 1 2229 16
Sensor 1: 1 1 2263 16
Sensor 1: 1 1 2269 16
Sensor 1: 1 1 2533 16
Sensor 2: 0 0 0 4
Sensor 2: 0 0 2100 4
Sensor 2: 0 1 1986 4
Sensor 2: 1 1 1689 4
Sensor 2: 1 1 1817 4
Sensor 2: 1 1 1931 4
Sensor 2: 1 1 1974 4

petrel.45df0631
Sensor 0: 0 0 2100 13
Sensor 1: 0 0 2100 11
Sensor 2: 0 0 2100 -23

petrel.d3ea0432
Sensor 0: 0 0 2100 -1
Sensor 1: 0 0 2100 -1
Sensor 2: 0 0 2100 -1

petrel.larrybainbridge (CCR)
Sensor 0: 0 1 2045 44
Sensor 1: 0 1 2025 -9
Sensor 2: 0 1 2045 51

petrel.marklee (CCR)
Sensor 0: 0 0 2100 -1
Sensor 1: 0 0 2100 -1
Sensor 2: 0 0 2100 -1

petrel.rainer (CCR, extppo2)
Sensor 0: 0 1 1990 0
Sensor 0: 0 1 2034 0
Sensor 0: 1 1 1671 0
Sensor 0: 1 1 1990 0
Sensor 0: 1 1 2034 0
Sensor 0: 1 1 2038 0
Sensor 0: 1 1 2112 0
Sensor 1: 0 1 1810 39
Sensor 1: 1 1 1810 39
Sensor 1: 1 1 1929 39
Sensor 1: 1 1 2007 39
Sensor 1: 1 1 2068 39
Sensor 1: 1 1 2326 39
Sensor 2: 1 1 1621 2
Sensor 2: 1 1 1866 2
Sensor 2: 1 1 1939 2
Sensor 2: 1 1 2010 2
Sensor 2: 1 1 2108 2

predator.janschubert (CCR, extppo2)
Sensor 0: 1 1 859 -16
Sensor 0: 1 1 866 -16
Sensor 0: 1 1 867 -16
Sensor 0: 1 1 868 -16
Sensor 0: 1 1 878 -16
Sensor 0: 1 1 879 -16
Sensor 0: 1 1 881 -16
Sensor 0: 1 1 888 -16
Sensor 0: 1 1 890 -16
Sensor 0: 1 1 892 -16
Sensor 0: 1 1 895 -16
Sensor 1: 1 1 812 -24
Sensor 1: 1 1 814 -24
Sensor 1: 1 1 819 -24
Sensor 1: 1 1 828 -24
Sensor 1: 1 1 829 -24
Sensor 1: 1 1 834 -24
Sensor 1: 1 1 839 -24
Sensor 1: 1 1 843 -24
Sensor 2: 1 1 827 -11
Sensor 2: 1 1 831 -11
Sensor 2: 1 1 832 -11
Sensor 2: 1 1 836 -11
Sensor 2: 1 1 837 -11
Sensor 2: 1 1 839 -11
Sensor 2: 1 1 841 -11
Sensor 2: 1 1 844 -11
Sensor 2: 1 1 845 -11
Sensor 2: 1 1 856 -11

predator.kasrafaghihi
Sensor 0: 0 0 0 0
Sensor 1: 0 0 0 0
Sensor 2: 0 0 0 0

predator.marklee (CCR, extppo2)
Sensor 0: 1 1 1069 -41
Sensor 0: 1 1 885 -41
Sensor 0: 1 1 904 -41
Sensor 0: 1 1 982 -41
Sensor 1: 1 1 1000 -39
Sensor 1: 1 1 1016 -39
Sensor 1: 1 1 989 -39
Sensor 1: 1 1 996 -39
Sensor 2: 1 1 1179 -5
Sensor 2: 1 1 1228 -5
Sensor 2: 1 1 1261 -5
Sensor 2: 1 1 1376 -5

As you can see, the ADC offset never changes! Only the calibration value 
changes, which is of course expected. The ADC offset values are not 
always close to zero (e.g. ranging from -41 to 51). And last but not 
least, the ADC offset value -1 is quite common. I suspect that this 
might be models which do not support external O2 sensors. In that case 
it makes sense to record the special value -1 to indicate "not 
available". The corresponding calibration value is always 2100, so I 
guess that's the factory default value.

Davide's data is the exception to the rule. It's the only dataset with 
CCR dives present, and an ADC offset of -1. I'm not sure what's going on 
there. The -1 could be a valid value here, but it would be really 
coincidence if all three sensors have the same ADC offset. All other 
datasets with CCR dives have different values for each sensor.

I suspect the millivolt values already take into account the ADC value. 
Because if that's not the case, then I would expect to see large deltas 
between the stored average ppO2 and the manually calculated ppO2 after 
doing the millivolt conversion. The larger the ADC offset (absolute 
value), the larger the delta. But the cases where I see a delta larger 
than 0.02 seems to be cases where one sensor is an outlier and was most 
likely voted out. But again Davide's dataset seems to be the exception 
here.

Jef
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